The present invention involves the field of surgery, and particularly orthopaedic surgery. The invention relates to surgical instruments and procedures involved in the distraction of adjacent tissue surfaces.
A variety of physical conditions involve two tissue surfaces that, for treatment of the condition, need to be distracted from one another and then supported away from one another. Such distraction may be to gain exposure to select tissue structures, to apply a therapeutic pressure to select tissues, to return tissue structures to their anatomic position and form, or in some cases to deliver a drug or growth factor to alter, influence or deter further growth of select tissues. Depending on the condition being treated, the tissue surfaces may be opposed or contiguous and may be bone, skin, soft tissue, or a combination thereof. An optimal treatment method includes distracting and supporting the tissue surfaces simultaneously.
A minimally invasive distraction and support device has significant application in orthopaedic surgical procedures, including acute and elective procedures to treat bone fractures and degenerative changes of the skeletal system and including vertebral compression fractures, interbody fusion, vertebral disc augmentation or replacement, and other compression fractures including, but not limited to tibial plateau compression fractures, calcaneous compression fractures, distal tibia fractures, distal radius (wrist) fractures, crushed or fractured orbit and orthopaedic oncology. Further, a minimally invasive distraction and support device has application in non-orthopaedic surgical procedures in plastic surgery (for example facial reconstruction), gastrointestinal surgery and urological surgery (for example the treatment of incontinence).
Vertebral Compression Fractures
A vertebral compression fracture is a crushing injury to one or more vertebrae. Vertebral fractures are generally associated with osteoporosis (the “brittle bone” disease), metastasis, and/or trauma. Osteoporosis reduces bone density, thereby weakening bones and predisposing them to fracture.
The osteoporosis-weakened bones can collapse during normal activity. In severe cases of osteoporosis, actions as simple as bending forward can be enough to cause a vertebral compression fracture. Vertebral compression fractures are the most common type of osteoporotic fractures according to the National Institute of Health. The mechanism of these fractures is one of flexion with axial compression where even minor events cause damage to the weak bone. While the fractures may heal without intervention, the crushed bone may fail to heal adequately. Moreover, if the bones are allowed to heal on their own, the spine will be deformed to the extent the vertebrae were compressed by the fracture. Spinal deformity may lead to breathing and gastrointestinal complications, and adverse loading of adjacent vertebrae.
Vertebral fractures happen most frequently at the thoracolumbar junction, with a relatively normal distribution of fractures around this point. Vertebral fractures can permanently alter the shape and strength of the spine. Commonly, they cause loss of height and a humped back. This disorder (called kyphosis or “dowager's hump”) is an exaggeration of the spinal curve that causes the shoulders to slump forward and the top of the back to look enlarged and humped. In severe cases, the body's center of mass is moved further away from the spine resulting in increased bending moment on the spine and increased loading of individual vertebrae.
Another contributing factor to vertebral fractures is metastatic disease. When cancer cells spread to the spine, the cancer may cause destruction of part of the vertebra, weakening and predisposing the bone to fracture. Osteoporosis and metastatic disease are common root causes leading to vertebral fractures, but trauma to healthy vertebrae also causes minor to severe fractures. Such trauma may result from a fall, a forceful jump, a car accident, or any event that stresses the spine past its breaking point. The resulting fractures typically are compression fractures or burst fractures.
Vertebral fractures can occur without pain. However, they often cause a severe “band-like” pain that radiates from the spine around both sides of the body. It is commonly believed that the source of acute pain in compression fractures is the result of instability at the fracture site, allowing motion that irritates nerves in and around the vertebrae.
Until recently, treatment of vertebral compression fractures has consisted of conservative measures including rest, analgesics, dietary, and medical regimens to restore bone density or prevent further bone loss, avoidance of injury, and bracing. Unfortunately, the typical patient is an elderly person who generally does not tolerate extended bed rest well. As a result, minimally invasive surgical methods for treating vertebral compression fractures have recently been introduced and are gaining popularity.
One technique used to treat vertebral compression fractures is injection of bone filler into the fractured vertebral body. This procedure is commonly referred to as percutaneous vertebroplasty. Vertebroplasty involves injecting bone filler (for example, bone cement) into the collapsed vertebra to stabilize and strengthen the crushed bone.
In vertebroplasty, physicians typically use one of two surgical approaches to access thoracic and lumbar vertebral bodies: transpedicular or extrapedicular. The transpedicular approach involves the placement of a needle or wire through the pedicle into the vertebral body, and the physician may choose to use either a unilateral access or bilateral transpedicular approach. The second approach, the extrapedicular technique, involves an entry point through the posterolateral corner of the vertebral body. The needle entry point is typically 8 cm to 12 cm lateral of the mid-sagittal plane, with the skin incision typically closer to 8 cm in the proximal spine and generally closer to 12 cm in the distal spine. In general, one cannula is placed to fill the vertebral body with the extrapedicular approach.
Regardless of the surgical approach, the physician generally places a small diameter guide wire or needle along the path intended for the bone filler delivery needle. The guide wire is advanced into the vertebral body under fluoroscopic guidance to the delivery point within the vertebrae. The access channel into the vertebra may be enlarged to accommodate the delivery tube. In some cases, the delivery tube is placed directly and forms its own opening. In other cases, an access cannula is placed over the guide wire and advanced into the vertebral body. After placement, the cannula is replaced with the delivery tube, which is passed over the guide pin. In both cases, a hollow needle or similar tube is placed into the vertebral body and used to deliver the bone filler into the vertebra.
In this procedure, lower viscosities and higher pressures tend to disperse the bone filler throughout the vertebral body. However, such conditions dramatically increase the risk of bone filler extravasation from the vertebral body. The transpedicular approach requires use of a relatively small needle (generally 11 gauge or smaller). In contrast, the extrapedicular approach provides sufficient room to accommodate a larger needle (up to 6 mm internal diameter in the lumbar region and lower thoracic regions). In general, the small diameter needle required for a transpedicular approach necessitates injecting the bone filler in a more liquid (less viscous) state. Further, the pressure required to flow bone filler through a small gauge needle is relatively high. The difficulty of controlling or stopping bone filler flow into injury sensitive areas increases as the required pressure increases. The larger needle used in the extrapedicular approach allows injection of bone filler in a thicker, more controllable viscous state. Therefore, many physicians now advocate the extrapedicular approach so that the bone filler may be delivered through a larger cannula under lower pressure.
Caution must be taken to prevent extravasation, with the greatest attention given to preventing posterior extravasation because it may cause spinal cord trauma. Physicians typically use fluoroscopic imaging to monitor bone filler propagation and to avoid flow into areas of critical concern. If a foraminal leak results, the patient may require surgical decompression and/or suffer paralysis.
Kyphoplasty is a modified vertebral fracture treatment that uses one or two balloons, similar to angioplasty balloons, to attempt to reduce the fracture and restore vertebral height prior to injecting the bone filler. Two balloons are typically introduced into the vertebra via bilateral transpedicular cannulae. The balloons are inflated to reduce the fracture. After the balloon(s) is deflated and removed, leaving a relatively empty cancellous bone, bone cement is injected into the vertebra. In theory, inflation of the balloons restores vertebral height. However, it is difficult to consistently attain meaningful height restoration. It appears the inconsistent results are due, in part, to the manner in which the balloon expands in a compressible media and the structural orientation of the trabecular bone within the vertebra.
Tibial Plateau Compression Fractures
A tibial plateau fracture is a crushing injury to one or both of the tibial condyles resulting in a depression in the articular surface of the condyle. In conjunction with the compression fracture, there may be a splitting fracture of the tibial plateau. Appropriate treatment for compression fractures depends on the severity of the fracture. Minimally displaced compression fractures may be stabilized in a cast or brace without surgical intervention. More severely displaced compression with or without displacement fractures are treated via open reduction and internal fixation.
Typically, the underside of the compression fracture is accessed either through a window cut (a relatively small resection) into the side of the tibia or by opening or displacing a splitting fracture. A bone elevator is then used to reduce the fracture and align the articular surface of the tibial condyle. Bone filler is placed into the cancellous bone under the reduced compression fracture to maintain the reduction. If a window was cut into the side of the tibia, the window is packed with graft material and may be secured with a bone plate. If a splitting fracture was opened to gain access, then the fracture is reduced and may be stabilized with bone screws, bone plate and screws, or a buttress plate and screws.
Spinal Interbody Fusion
Spinal fusion is most frequently indicated to treat chronic back pain associated with instability or degenerative disc disease that has not responded to less invasive treatments. Fusion is also prescribed to treat trauma and congenital deformities. Spinal fusion involves removal of the spinal disc and fusing or joining the two adjacent vertebrae. The primary objective for patients suffering from instability is to diminish the patient's pain by reducing spinal motion.
Spinal fusions are generally categorized into two large groups: instrumented and non-instrumented. In non-instrumented procedures, the physician removes tissue from the unstable disc space and fills it with some form of bone graft that facilitates the fusion of the two adjacent vertebral bodies. Instrumented procedures are similar to non-instrumented procedures, except that implants (generally metallic) are also applied to further stabilize the vertebrae and improve the likelihood of fusion.
Conventional instrumented procedures generally utilize plates, rods, hooks, and/or pedicle screws through various surgical approaches. These conventional implants are secured to the vertebral bodies that are being fused. Interbody fusion devices were introduced in the 1990's as a less invasive surgical alternative, although interbody devices are increasingly being used in conjunction with pedicle screws. Interbody devices are implanted into the disc space to restore the normal disc spacing, utilizing tension in the annulus to stabilize the fusion unit. Interbody fusion provides a large area of the vertebral end plate for establishing bony fusion, a viable blood supply from the decorticated end plates, and dynamic compressive loading of the graft site. The interbody devices are generally filled with a bone filler to facilitate fusion. Interbody devices can be categorized in three primary groups: spinal fusion cages, which are available in a variety of shapes including rectangular, round-faced, and lordotic; allograft bone dowels and wedges (which are also available in various shapes); and titanium mesh (although titanium mesh is not itself a structural spacer).
Interbody fusion is typically completed through a posterior, an anterior, or a lateral inter-transverse approach. Each of these techniques has limitations. Lumbar interbody fusion presents a challenging surgical procedure and relatively high pseudoarthrosis rates. As a result, this approach is increasingly combined with additional internal fixation devices such as pedicle screw fixation.
In all interbody surgical approaches, a relatively large opening is made in the annulus. The nuclear material is removed and the end plates are decorticated to facilitate bony fusion. Overall, the use of interbody devices has resulted in mixed clinical outcomes. Placement of a fixed height device presents challenges in proper tensioning of the annulus. For these and other reasons, there is concern over long-term stability of interbody devices and fusion mass.
Distraction Systems and Methods
One approach to address the concerns in the various surgical procedures discussed above is presented in U.S. Pat. No. 6,595,998, which issued on Jul. 22, 2003, and which is owned by the assignee of the present invention. The disclosure of the '998 Patent is expressly incorporated herein by reference. The system in the '998 Patent provides a combination of a temporary or long term implantable device and instrumentation to place the device, in which tissue surfaces are distracted along an axis to enable access to the space between the tissues. Generally, the '998 Patent discloses solid wafers for stacking upon one another to provide an axially extending column to distract and support tissue surfaces. While a primary use of that invention is to reduce and stabilize vertebral compression fractures, the disclosed devices and methods may be used in any situation where it is desirable to distract two tissue surfaces. The tissues may be bone, skin, soft tissue, or combinations thereof. Further, the surfaces may be opposed surfaces of contiguous elements or surfaces of opposed elements. The '998 Patent discloses devices and methods that may be used to treat vertebral compression fractures, for replacement of vertebral discs, as an interbody fusion device, wedge opening high tibial osteotomy, tibial tuberosity elevation, as well as for treating other compression fractures including, but not limited to tibia plateau fractures, calcaneous, distal tibial fractures, or distal radius (wrist) fractures.
The '998 Patent concerns a distraction device or solid scaffold or support structure that includes a plurality of stackable wafers designed for insertion between tissue surfaces to form a column. The wafer column is assembled percutaneously in vivo to provide a distraction force as well as support and stabilization of the distracted tissue. Preferably, the wafers place distraction force in one direction only and thus provide directional distraction. The distraction device may be permanently implanted, in which case the wafer column may be used alone or in conjunction with a bone filler material. Alternately, the distraction device may be used temporarily to manipulate tissues and then removed.
In use, the wafers are preferably stacked between two tissue surfaces as they are implanted, thereby distracting and supporting the tissue surfaces simultaneously. Use of the devices and methods of the '998 Patent to treat a vertebral compression fracture is depicted in FIG. 1. A series of wafers 11 are transported through a working channel cannula 15 into the cancellous bone C of a vertebral body V1. The wafers 11 are continually inserted into the cancellous bone, distracting the superior and inferior bony surfaces of the vertebral body V1 as the stack 10 of wafers grows. The wafers may be used to distract other tissue surfaces, such as between the tibial plateau and associated condyle.
In one embodiment, the wafers are designed to be beveled at both their leading and trailing edges so that when lined up end-to-end, force on the trailing edge of the trailing wafer causes its leading edge to slide below the trailing edge of the leading wafer, thereby lifting up the leading wafer. Likewise, the bevel of the leading and trailing edges may be reversed enabling insertion of a trailing wafer above a leading wafer. Alternately, the leading and trailing edges may be chevron shaped or curved when viewed from the side, enabling insertion of trailing wafers between any two leading wafers or on the top or bottom of the column. In another embodiment, the wafers may be configured with blunt edges wherein the wafers are stacked with the insertion instrument. In all embodiments, by repeating the process with consecutive wafers, the column height increases to restore vertebral height.
In order to place the wafers between the tissue surfaces, the '998 Patent discloses a wafer inserter 12, as depicted in FIG. 2, that includes the track 13 positioned within the surgical site with access at its distal tip to the tissue surfaces to be distracted and supported. Wafers can be fed from a cartridge 14. As disclosed in the '998 Patent, the inserter includes a plunger is that is used to advance the wafer to the distal end of the cannula. This is repeated with consecutive wafers until a column of sufficient height is created per physician discretion. After the wafer(s) have been inserted, the insertion device is removed. The distal end of the insertion device may be manufactured from the same material as the wafers and/or be detachable. In this embodiment, the distal end of the insertion instrument would be detached after placing the wafer column, and the instrument removed.
The wafers disclosed in the '998 Patent may be formed from a solid form of bone filler material, and/or any other suitable material such as but not limited to implantable grade alloys (including, but not limited to titanium, cobalt chrome, nitinol, or stainless steel), other medical grade composites (including, but not limited to polyetheretherketone polymer (PEEK), ultra-high molecular weight polyethylene, or polyethylene) other ceramics (including, but not limited to zirconia, alumina, or calcium-phosphate based ceramics), and resorbable polymers (for example, polylactic acid (PLA), polyglycolic acid (PGA), and poly(lactide-coglycolide) (PLGA)). The wafers may be dense or porous, while porous wafers may be filled with resorbable polymers to increase mechanical strength. For soft tissue applications, it may be desirable to manufacture the wafers of woven collagen pads, tissue engineered materials, chitin, urethanes, silicone, or silicone materials. Alternately, the wafers may be manufactured from hydrogel (polyvinyl alcohol) in which the wafer is inserted in a dehydrated form and expands with fluids present at the insertion site. Hydrogel wafers may be particularly desirable for placing in the disc space between vertebrae. For purposes of this disclosure, these materials and their combinations will be collectively defined as the “implant materials.”
Further, the wafers and implant materials may be combined with osteoinductive agents (including BMPs, growth factors, cell therapy, gene therapy, and patient derived factors) and other drug therapies. The osteoinductive agents may be added to initiate and accelerate bone formation while the drug therapies may range from antibiotics to reduce the risk of infection to chemotherapy to treat cancer. Optionally, the wafers may be used with a flowable bone filler material, which may be defined as any substance used to stabilize the bone. Suitable bone filler material includes, but is not limited to, bone cement (polymethyl methacrylate PMMA, or PMA), other composite material, human bone graft (allograft or autograft), synthetic and xenograft derived bone substitutes (calcium phosphate, hydroxylapatite, and/or other ceramic based bone substitutes), collagen, or combinations of these materials.
It is disclosed in the '998 Patent that in certain applications, it may be beneficial for the wafers to be secured to one another after insertion. Any suitable method for securing the wafers to one another as known by those skilled in the arts may be used. Wafers may be secured to one another by means of an adhesive bond, a chemical bond, and/or a mechanical interlock (as described above). Applying a generic fluent adhesive, for example cyanoacrylate, around the column provides adhesive bonding. The fluent adhesive hardens and locks the wafers.
Introducing a liquid material that is chemically equivalent to the wafer provides a potential chemical bonding. For example, the wafers may be manufactured from bone cement and bone cement may be injected around the wafers and into the vertebral body. The monomer in the bone cement may initiate a chemical bonding between the wafer and the bone filler, thereby locking the wafers together. A stable construct combined with cement interdigitation is believed to provide stability and pain relief in a crushed vertebra.
The devices and methods of the '998 Patent address various inabilities in the prior art to adequately distract opposing tissue surfaces. The devices disclosed in the '998 Patent are particularly beneficial in restoring the vertebral body to its intended anatomic height following a compression fracture. However, even with this improvement, there still remains a need for devices and methods for introducing fluent or liquid material into the distraction site, and particularly adjacent to or around the height restoring or load bearing distraction component. The fluent material may itself provide structural or load bearing capabilities, or may be non-structural but still capable of alleviating pain associated with the fracture.